There is a practice of performing pathological diagnosis to identify the type, characteristic, and the like of a lesion by checking part of a tissue harvested from a patient. In such pathological diagnoses, it is necessary to observe the microstructure of a tissue segment in more detail at the microlevel with a microscope (this operation will be referred to as micro-observation or micro-diagnosis hereinafter). An optical microscope has been an especially important tool for pathologists. In addition, when performing micro-diagnosis by the naked eye with a microscope, it is often a case that pathologists want to record important finding images as evidence. For this reason, an optical microscope is equipped with a digital camera to be used for recording finding images. It is also possible to use digital scanners and digital microscopes incorporating digital cameras (image sensing devices).
When performing a morphological diagnosis, a functional diagnosis, and capturing an evidence image with a digital camera in a pathological diagnosis, it is required to easily reproduce an observation position. The structures in a cell are distributed in the μ to sub-μ range. An irregular shape observed in this case can be regarded as an ROI with the minimum size obtained by pathological diagnosis. An objective lens for visible light used in general has a resolution of about 0.2 μm (with 550-nm green light) at 100×. An objective lens for ultraviolet light can resolve up to about 0.1 μm (with 200-nm ultraviolet light). Assuming, therefore, that the minimum size of an ROI is, for example, 1 μm square, which is 10 times 0.1 μm, which is the ultraviolet resolution limit, it can be expected that a target accuracy in observation position management will be set to 0.1 μm, which is the resolution limit, and a unit of coordinate management will be set to 0.01 μm, which is 1/10 the target accuracy. The movement of an observation position is implemented by an XY stage on which a slide is placed and which can move in the X and Y directions perpendicular to the optical axis direction. Therefore, it is required to implement the accurate observation position management described above for an XY stage mounted on a microscope. An XY stage aiming at implementing accurate observation position management (Japanese Patent Laid-Open No. 11-231228 (to be referred to as patent literature 1 hereinafter), Japanese Patent Laid-Open No. 2014-010354 (to be referred as patent literature 2 hereinafter), and Japanese Patent Laid-Open No. 2010-175850 (to be referred to as patent literature 3 hereinafter)).
In observation position management for an XY stage, an XY position is detected by reading a scale, which moves together with an X stage or Y stage, with a sensor. In general, a sensor for reading a scale fixed to an X stage (or Y stage) is fixed to the Y stage (or base stage). However, when the sensor position varies due to the thermal expansion or the like of the stage, the variation appears as an error in an XY position, which can be an error which cannot be neglected when implementing an accuracy on the order of 0.01μ, as described above.
Although the optical axis of a microscope coincides with a sensor position, the sensor is robust against the influence of expansion caused by a temperature change, an optical microscope has an opening portion in an optical axis portion, and hence a sensor cannot be fixed near the optical axis. If the sensor is arranged avoiding the opening portion, since the fixing position of the sensor is separated from the optical axis, enlargement/contraction of the stage caused by a temperature change causes an error in the read position of the stage.
Patent literatures 1 to 3 each describe an apparatus which automatically moves the XY stage of a microscope, but give no consideration to temperature compensation for position control (observation position management) of the XY stage. For example, patent literatures 1 and 3 each disclose a method of automatically moving the XY stage, but pay no attention to the problem that when the stage expands or contracts due to a temperature change, the position of the sensor itself shifts. In addition, the microscope apparatus disclosed in patent literature 2 can reduce the influence of thermal expansion caused by a temperature change in the focus direction. However, this literature describes nothing about temperature compensation in position control of the XY stage in the X and Y directions.